Electroacoustic transducer



May 9, 1967 FIMASSRJiR 3,31

I ELECTROACOUSTIC TRANSDUCER Filed March 29, 1965 IV l/E/VTOR. F/M A/K M45514, JP.

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3,319,219 Patented May 9, 1967 ice 3,319,219 ELECTROACOUTHC TRANSDUCER Frank Massa, .Iix, Cohassct, Mass, assignor to Massa illafiivision, Dynamics Corporation of America, I-lingham,

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Filed Mar. 29, 1965, fier- No. 443,496 13 Claims. (Cl. 340-8) This invention relates generally to transducers and, more particularly, to transducers capable of operation in very deep water. Heretofore, transducers designed for operation in deep water have been designed so that the high hydrostatic pressure at great depths is transferred to the transducer material which is employed in the transducer. In some designs, pressure equalization has been achieved by oil filling the transducer so that the hydrostatic pressure in the deep water is transferred through a rubber window to the oil filling within the structure.

Earlier transducers required to operate down to depths of the order of 1,000 feet or less could resist the corresponding hydrostatic pressure without appreciable change in their operating characteristics. However, as deeper submergence became necessary, the high hydrostatic pressure associated with very deep submergence, generally caused variations in the operating characteristics of the transducer and, in some cases, the high pressures, corresponding to very deep water operation, caused extreme nonlinearity in the operating characteristics and, sometimes, even rendered the transducer efiectively inoperative.

In order to overcome the limitations, and to provide a transducer whose operating characteristics will not change with depth, even when operating under very high hydrostatic pressure corresponding to water depths far in excess of 1,000 feet, I have designed a transducer structure in which the exposed radiating portion of the diaphragm is capable of resisting the extremely high hydostatic pressures corresponding to the desired depths of operation. The operating part of the transducer is kept at its normal shallow water stresses since the operating structure is not influenced by the external pressure imposed on the transducer assembly.

A primary object of this invention is to provide a novel transducer for operating in very deep water in excess of 1,000 feet, such transducer having operating characteristics that are not influenced by the depth of submergence.

Another object of this invention is to provide a low cost transducer assembly in which the diaphragm portion of the transducer becomes a pressure seal when the transducer is assembled to close the open end of a pressureproof housing.

A further object of this invention is to provide a transducer design for use in very deep water (in excess of 1,000 feet) that does not require any pressure equalization and in which the diaphragm portion resists the full hydrostatic pressure corresponding to the depth of submergence of the transducer.

An additional object of this invention is to provide a transducer with a sectionalized diaphragm design such that multiple resonances may be achieved and high efiiciencies may be realized at different operating frequencies.

These and other objects of the invention will become evident in the following detailed description. The novel features which are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as advantages thereof, will best be understood from the following description of several embodiments thereof when read in connection with the accompanying drawings, in which:

FIGURE 1 is a vertical section illustrating one form of the invention;

FIGURE 2 is a vertical section illustrating another form of the invention;

FIGURE 3 is a simplified equivalent circuit diagram for the purpose of illustrating the operation of the transducer in FIGURE 1;

FIGURE 4 is a simplified equivalent circuit diagram to illustrate the operation of the transducer shown in FIGURE 2; and

FIGURE 5 is a simplified equivalent electrical circuit diagram illustrating the operation of the transducer at its highest required frequency region of operation.

Turning now to the drawing and more specifically to FIGURE 1, there is shown one illustrative transducer construction embodying the present invention. The transducer assembly 10 is preferably of the inertia type and includes an inertial mass element 11 bonded by a suitable cement 12, such as epoxy, to one end of a polarized ceramic cylinder 13. The opposite end of the ceramic cylinder 13 is bonded to the bottom plane surface of the center portion 14 of a diaphragm structure 15 by a suitable cement 2. For purposes of illustration, the piezoelectric ceramic cylinder 13- may consist of polarized barium titanate or polarized lead zirconate titanate having electrodes 16 and 17 arranged on the surfaces shown for the well known purpose of permitting the material to vibrate along its cylindrical axis when electrical alternating voltages are applied to the electrode surfaces. Insulated electrical conductors 18 and 19 are attached to the electrodes 16 and 17, as illustrated, as for example, by soldering, in order to establish electrical connection to the transducer. Although the transducer is illustrated as using a polarized ceramic cylinder as the active element, it is well known by those skilled in the art that the ceramic could be replaced by other transducer materials, such as magnetostrictive elements or piezoelectric crystal plates, as for example, as is shown in FIG- URE 3 of the copending United States patent application Ser. No. 173,510, filed Feb. 15, 1962, by Frank Massa, now abandoned.

The diaphragm structure 15 is provided with a peripheral portion 25 having a groove 20 therein forreceiving an O-ring 21 which achieves a pressure seal when the diaphragm 15 is attached to close the open end of pressure housing 22 by means of the screws 24.

The housing structure 22 may comprise a tubular sleeve member made from aluminum or magnesium alloy. The end of the housing 22 remote from the diaphragm may be afiixed to a multiple transducer head assembly or the end may be closed by conventional sealing means to provide a sealed waterproof enclosure about the transducer.

The diaphragm 15 is undercut as shown in FIGURE 1 to provide an annular, web-like portion 23. Preferably, the diaphragm is made from metal. The top of the groove or undercut in the diaphragm is inclined inwardly and upwardly toward the axis of the housing 22 in order to achieve approximately constant stress distribution in the web, thereby realizing maximum strength for a desired value of compliance. This construction localizes the central piston portion 14 of the diaphragm and enables the web 23 to serve as a compliant link between the central piston portion 14 of the diaphragm and the remainder of the diaphragm structure. The configuration of the undercut is important in order to provide a diaphragm having desired operating characteristics and sufficient strength to provide for operation of the transducer assembly at very great depths in water, for example, below 1,000 feet. The structure of the compliant web portion 23 is made adequate to withstand the maximum hydrostatic pressure to which the transducer is subjected. At the same time the compliance of the web is sufficiently high that the vibration of the piston portion 14 for its desired frequency of operation is effectively uncoupled from the outer portion of the diaphragm assembly and housing structure. Preferably, the web or compliant member 23 is capable of withstanding hydrostatic pressures in excess of 1,000 p.s.i.

As an alternate construction, housing 22 and diaphragm 15 may be formed from a solid metallic plate member in which the web portion 23 is machined out from the solid plate member. By this arrangement, there will be no need for either the O-ring seal 21 or the screws 24.

A relatively lightweight, thin wall dust cover 26 which may be of flexible plastic is provided to enclose the internal transducer assembly as illustrated in the drawing. The dust cover may have an interference fit so that it tightly fits over the periphery of the center piston portion 14 of the diaphragm.

In order to give a more complete understanding of the relationships between the mechanical constants of the various coupled parts of the transducer, a simplified equivalent electrical circuit is shown in FIGURE 3. The oscillatory force generated within the ceramic element 13 is illustrated by 1. C represents the compliance of the ceramic; m represents the mass of the inertial element 11; m represents the mass of the piston portion 14 of the diaphragm structure; r represents the radiation resistance presented by the water to the vibrating piston portion 14; C represents the compliance of the web member 23; and m represents the effective combined mass of the peripheral portion 25 of the diaphragm structure 15 plus the assembeld housing structure 22.

The equivalent circuit diagrams are used only to illustrate the operation of the transducer and the invention is not dependent on the validity of these diagrams. The novel transducer described in this application has successfully operated in water depths in excess of 15,000 feet.

For the idealized condition, m (the mass of the peripheral portion 25 of diaphragm 15 and of the assembled housing structure 22) is made as large as possible and the magnitude of the compliance C of the web member 23 is made as high as possible. When these objectives are achieved, the impedance of 111 becomes very large and the impedance of compliance C becomes very low. Thus m and C can be eliminated from consideration and this reduces the equivalent circuit of FIG- URE 3 to the circuit shown in FIGURE 5. Under these conditions, the resonant frequency of the transducer will be determined by the compliance of the transducer material C and the magnitude of the inertial mass m and the piston portion 14 represented by m r represents the radiation resistance of the medium into which the acoustic energy is transmitted.

FIGURE 2 shows another form of this invention. Two annular grooves or undercuts 35 and 36 are machined into the diaphragm structure 15' as shown to form two concentric webs 31 and 33. The undercut 35 has a top portion inwardly and upwardly inclined with respect to the longitudinal axes of the transducer and of the housing structure. The web-like portion 31 defined between central piston portion 34 and depending ring portion 32 is constructed and arranged to provide sufficient diaphragm strength for operation at great depths in the water, as well as provide the desired operating characteristics. An annular ring portion 32, which defines a mass later referred to as m remains between the two concentric web portions 31 and 33. The transducer is similar to the transducer illustrated in FIGURE 1 and, accordingly, like numerals have been applied to like elements. The outer peripheral portion 35 of the diaphragm structure 15 is secured with a pressure seal or O-ring 21 to the open end of housing 11 the same as was described in FIGURE 1. The only difference in the design illustrated in FIGURE 2 is that the mass member 32 is interposed between the vibrating central piston portion 34 and the outer web portion 33.

An approximate equivalent electrical circuit to illustrate the operation of the design illustrated in FIGURE 2, is shown in FIGURE 4. The additional ring member 32 and the web 34 are represented by the inductance m and capacitance C respectively, in FIGURE 4. r represents the radiation resistance presented to the annular portion of the exposed area of the diaphragm.

At the highest frequency of operation, as represented by the resonant frequency of C together with the masses m and m the magnitude of the compliance C of the web member in FIGURE 4 is made sulficiently high so that its impedance acts effectively as a short circuit for the elements shown to the right of the equivalent circuit and for this condition, the transducer of FIGURE 2 reduces to the same equivalent circuit as shown in FIG- U'RE 5.

At a frequency lower than the highest resonant frequency region of operation, the impedance of C increases and at a specific frequency, the combination of the masses m and m will resonate with the compliance C at which point a high efliciency will be achieved and the transducer will have a high sensitivity at this particular lower frequency of resonance. The advantage of this lower frequency region of high sensitivity is particularly desirable for deep water oceanographic buoys in which a command signal may be sent to the submerged buoy by a distant ship, which can achieve a greater range at the lower frequency.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and therefore, it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An improved electroacoustic transducer assembly for converting electrical energy into vibrational energy and capable of operating under water comprising the combination of a sealed waterproof housing means, a transducer element having opposed extended surfaces, a diaphragm structure having a peripheral portion and a vibratile portion, a compliant member connecting said peripheral portion to said vibratile portion, said vibratile portion being vibratile along an axis independently from said peripheral portion, an inertial mass member, means for attaching one surface of said transducer element to said mass member, means for attaching the other of said opposed surfaces of said transducer element to said vibratile portion of said diaphragm structure, said inertial mass member and said transducer element being effectively supported for free movement with respect to said housing means, and electrical conductor means connected to said transducer element.

2. The invention as set forth in claim 1 further characterized in that said compliant member constitutes the sole support of said vibratile portion against hydrostatic pressure exerted by said water.

3. The invention as set forth in claim 2 further characterized in that said compliant member is constructed and arranged with sufficient compliance so that the vibration of the vibratile portion of said diaphragm structure is effectively uncoupled from the peripheral portion of said diaphragm structure at the operating frequency of the transducer assembly.

4. The invention as set forth in claim 2 further characterized in that the magnitude of the compliance of said compliant member is sufiiciently high so that the vibration of the vibratile portion of said diaphragm structure is effectively uncoupled from the peripheral portion of said diaphragm structure at the operating frequency of the transducer, the resonant frequency of the center vibratile portion in combination with said compliant member lying below the resonance frequency of the center vibratile portion in combination With the mass member and the transducer element.

5. A transducer assembly as set forth in claim 1 wherein the thickness of said compliant member increases with increasing distance from said vibratile portion.

6. An improved electroacoustic transducer assembly for operating under water at depths in excess of 1,000 feet comprising a housing member, a transducer element having opposed parallel plane surfaces, a diaphragm structure having a peripheral portion and a center vibratile portion, a compliant member connecting said peripheral portion to said vibratile portion, said vibratile portion constructed and arranged for vibration along an axis independently from said peripheral portion, said vibratile portion having a plane surface at right angles to the axis of vibration of said vibratile portion, an inertial mass member having a plane surface, means for attaching one plane surface of said transducer element to said plane surface of said mass member, means for attaching the other parallel plane surface of said transducer element to said plane surface of said vibratile portion of said diaphragm structure, said inertial mass member and said transducer element being effectively supported by said central vibratile port-ion of said diaphragm for free movement with respect to said housing member, and electrical conductor means connected to said transducer element, said peripheral portion of said diaphragm structure cooperating with said housing member to form a waterproof enclosure for said transducer element.

7. An improved electroacoustic transducer assembly for operating under water at depths in excess of 1,000 feet comprising a housing member, a transducer element having a pair of opposite parallel plane surfaces, a unitary diaphragm structure having a peripheral portion and a center vibratile portion, a compliant web member connecting said peripheral portion to said center portion, said center portion constructed and arranged for vibration along an axis independently from said peripheral portion, said center portion having a plane surface at right angles to the axis of vibration of said center portion, an inertial mass member having a plane surface, means for attaching one plane surface of said transducer element to said plane surface of said mass member, means for attaching said opposite parallel plane surface of said transducer element to said plane surface of said vibratile portion of said diaphragm structure, said transducer element and said inertial mass member being effectively supported for free movement with respect to said housing, said transducer element including a pair of electrode elements adapted to have an alternating voltage applied thereto for causing corresponding alternating mechanical vibrations to be set up in said transducer element, and electrical conductor means connected to said transducer element, said peripheral portion of said diaphragm structure cooperating with said housing member to form a waterproof enclosure for said transducer element, said compliant web member being thinner than said adjacent peripheral portion and center vibratile portion, said complaint web member being capable of withstanding hydrostatic pressure in excess of 1,000 p.s.i.

8. An improved electroacoustic transducer assembly operable in water at depths in excess of 1,000 feet, comprising a shell-like housing structure having a closed end, said closed end having an outer surface and an inner surface, a rigid piston-like secti-On comprising the center portion of said closed end, a web-like peripheral portion thinner than said piston-like center section which is contiguous to and surrounds said piston-like section, said web-like portion forming a continuing sealed portion of said shell-like housing, transducer means including a transducer element capable of converting electrical oscillations into mechanical vibrations, means for attaching said transducer element to the inner surface of said piston like section whereby mechanical vibrations of said transducer element will be transmitted to said piston-like section, said web-like peripheral portion of said housing structure, said transducer element being mounted for free movement with respect to said housing structure, having a stiffness such that the exposure of the external surface of said closed end to hydrostatic pressures in the region of a few thousand pounds per square inch will result in negligible deflection of said piston-like portion.

9. The invention set forth in claim 8 further characterized in that the resonant frequency of the mass of said piston-like section in combination with the stiffness of said web-like portion lies below the resonant frequency of the transducer means.

10. An improved transducer assembly for operation in deep water and adapted for insertion into an opening in a housing structure which comprises, in combination, a diaphragm member having a central section surrounded a plurality of annular sections, each of said sections being connected to its neighboring section by an annular web, the outer section of said diaphragm being affixed to said opening in said housing structure to form a waterproof enclosure, an inertial mass, an electroacoustic transducer having first and second surfaces, means for acoustically bonding said first surface to said central section of said diaphragm, means for acoustically bonding said second surface to said inertial mass, and means including said acoustic bonding means for supporting said transducer and said mass for free movement with respect to said housing structure as said central section is deflected due to hydrostatic pressure exerted by said deep water whereby undesirable compression of said transducer is eliminated.

11. The invention set forth in claim 10 further characterized in that said diaphragm portion comprises a center piston portion surrounded by two concentric annular portions and the three diaphragm portions are mechanically connected by two compliant web members.

12. The invention set forth in claim 11 characterized in that said web members constitute the sole support of said central section against hydrostatic pressures exerted by said deep water.

13. A transducer assembly as set forth in claim 10 wherein the thickness of each of said annular sections increases with increasing distance from said central section.

References Cited by the Examiner UNITED STATES PATENTS 1,075,949 10/1913 Smith 18l.5 X 1,604,693 10/1926 Hecht 3408 2,425,594 8/ 1947 Brown 34010 2,560,066 7/ 1951 Batchelder.

2,733,423 1/1956 Camp 340-10 2,745,083 5/1956 Snavely 3408 2,979,690 4/1961 Hackley 340-14 2,983,901 5/1961 Paslay et al 340l4 CHESTER L. JUSTUS, Primary Examiner.

G. M. FISHER, B. L. RIBANDO, Assistant Examiners. 

1. AN IMPROVED ELECTROACOUSTIC TRANSDUCER ASSEMBLY FOR CONVERTING ELECTRICAL ENERGY INTO VIBRATIONAL ENERGY AND CAPABLE OF OPERATING UNDER WATER COMPRISING THE COMBINATION OF A SEALED WATERPROOF HOUSING MEANS, A TRANSDUCER ELEMENT HAVING OPPOSED EXTENDED SURFACES, A DIAPHRAGM STRUCTURE HAVING A PERIPHERAL PORTION AND A VIBRATILE PORTION, A COMPLIANT MEMBER CONNECTING SAID PERIPHERAL PORTION TO SAID VIBRATILE PORTION, SAID VIBRATILE PORTION BEING VIBRATILE ALONG AN AXIS INDEPENDENTLY FROM SAID PERIPHERAL PORTION, AN INERTIAL MASS MEMBER, MEANS 